The influence of different types of SCMs on microstructure and macroscopic properties of cementitious materials

Abstract

In our study, the influence of different supplementary cementitious materials (SCMs) such as metakaolins, silica fume (microsilica) or filtered coal fly ash on the performance of concrete is discussed. The effects of different types and dosages of the SCMs have been investigated. Centrilit NC (MK1) and Metaver N (mk2) type metakaolins, Microsit® 20 (MS) type filtered coal fly ash or Centrilit Fume SX (SF) silica fume suspension was chosen as the replacement for the CEM I 42.5 N-SR0 sulphate resistant Portland cement. In addition to the two-component mixtures, we also examined the behaviour of the ternary blends, i.e. the combinations of SCMs. For the experiments, mortar prisms and cylindrical mortar specimens were prepared with water to binder ratio of 0.4. The paper presents the test results performed up to two years. The compressive strengths of the mixtures were examined. The most critical property of the cement-bound materials, the chloride migration coefficient of each mixture, was determined. The microstructure of the mixtures was determined by mercury intrusion porosimetry at the age of one year. Our results indicated (i) the best compressive strength was achieved for MK2 and for MK1 with combination of SF; (ii) the pore structure is much finer in the case of MK1 mixtures compared with those of MK2 or MS mixtures; (iii) the whole most frequent pore diameter interval falls into the range of medium capillaries only in case of MK1 (10 w%), for other mixtures the large capillaries are present in different extent. The SCMs greatly influence the extent of the enhancement in chloride migration coefficients with age: the less reduction was found for the mixtures of MK1, and the highest reduction was found for mixtures of MS. There is no direct function between the compressive strength, total porosity, specific surface of porosity or chloride migration coefficients.